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| United States Patent |
5,275,988
|
|
Mori
, et al.
|
January 4, 1994
|
Ceramic composition
Abstract
A ceramic composition is herein disclosed, which is a lead-type perovskite
compound capable of being subjected to low temperature-sintering among
ceramic compositions for use in making capacitors, which has a high
dielectric constant at room temperature of not less than 10000, a low
temperature-dependency of the dielectric constant and a low decrease in
capacitance upon application of a DC bias and which comprises, as a main
constituent, a ternary system comprising lead magnesium niobate:
[Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ], lead nickel niobate: [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ] and lead titanate: [PbTiO.sub.3 ] in which part of
the Pb.sup.2+ ions present in the ternary system are substituted with a
desired amount of Sr.sup.2+ ions, Ba.sup.2+ ions or Ca.sup.2+ ions.
| Inventors:
|
Mori; Toru (Tokyo, JP);
Furuya; Mitsuru (Tokyo, JP);
Ochi; Atsushi (Tokyo, JP)
|
| Assignee:
|
NEC Corporation (Tokyo, JP)
|
| Appl. No.:
|
865445 |
| Filed:
|
April 9, 1992 |
Foreign Application Priority Data
| Apr 12, 1991[JP] | 3-106469 |
| Apr 12, 1991[JP] | 3-106470 |
| Nov 28, 1991[JP] | 3-337864 |
| Current U.S. Class: |
501/136; 501/135 |
| Intern'l Class: |
C04B 035/46 |
| Field of Search: |
501/135,136,139,137
|
References Cited
U.S. Patent Documents
| 4712156 | Dec., 1987 | Bardham | 501/135.
|
| 4751209 | Jun., 1988 | Yokotani et al. | 501/138.
|
| Foreign Patent Documents |
| 2-009760 | Jan., 1990 | JP.
| |
Primary Examiner: Bell; Mark L.
Assistant Examiner: Jones; Deborah
Attorney, Agent or Firm: Leydig, Voit & Mayer
Claims
What is claimed is:
1. A ceramic composition comprising, as a main constituent, a ternary
system essentially consisting of lead magnesium niobate, [Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3 ], lead nickel niobate, [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ] and lead titanate. [PbTiO.sub.3 ] and being expressed
by the following general formula [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x
[Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z wherein the
subscripts x, y and z satisfy the following relation: x+y+z=1.0 and fall
within the area defined by the line segments joining the following seven
points (a) to (g) which are given by the coordinates:
______________________________________
(x = 0.10, y = 0.70, z = 0.20) (a)
(x = 0.10, y = 0.475, z = 0.425) (b)
(x = 0.625, y = 0.05, z = 0.325) (c)
(x = 0.75, y = 0.05, z = 0.20) (d)
(x = 0.75, y = 0.15, z = 0.10) (e)
(x = 0.50, y = 0.40, z = 0.10) (f)
(x = 0.15, y = 0.70, z = 0.15) (g)
______________________________________
on the triangular ternary-system diagram; and wherein part of Pb.sup.2+
ions of the main constituent are substituted with 0.01 to 30 mole % of
strontium ions (Sr.sup.2+).
2. The ceramic composition of claim 1 wherein the amount of Sr.sup.2+
-substitution ranges from 2 to 20 mole %.
3. A ceramic composition comprising, as a main constituent, a ternary
system essentially consisting of lead magnesium niobate, [Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3 ], lead nickel niobate, [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ], and lead titanate, [PbTiO.sub.3 ], and being
expressed by the following general formula: [Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.y
[PbTiO.sub.3 ].sub.z wherein the subscripts x, y and z satisfy the
following relation: x+y+z=1.0 and fall within the area defined by the line
segments joining the following seven points (a) to (g) which are given by
the coordinates:
______________________________________
(x = 0.10, y = 0.70, z = 0.20) (a)
(x = 0.10, y = 0.475, z = 0.425) (b)
(x = 0.625, y = 0.05, z = 0.325) (c)
(x = 0.75, y = 0.05, z = 0.20) (d)
(x = 0.75, y = 0.15, z = 0.10) (e)
(x = 0.50, y = 0.40, z = 0.10) (f)
(x = 0.15, y = 0.70, z = 0.15) (g)
______________________________________
on the triangular ternary-system diagram; and wherein part of Pb.sup.2+
ions of the main constituent are substituted with 0.01 to 25 mole % of
barium ions (Ba.sup.2+).
4. The ceramic composition of claim 3 wherein the amount of Ba.sup.2+
-substitution ranges from 2 to 20 mole %.
5. A ceramic composition comprising, as a main constituent, a ternary
system essentially consisting of lead magnesium niobate [Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3 ], lead nickel niobate, [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ], and lead titanate [PbTiO.sub.3 ] and being expressed
by the following general formula: [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
].sub.x [Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z
wherein the subscripts x, y and z satisfy the following relation:
x+y+z=1.0 and fall within the area defined by the line segments joining
the following seven points (a) to (g) which are given by the coordinates:
______________________________________
(x = 0.10, y = 0.70, z = 0.20) (a)
(x = 0.10, y = 0.475, z = 0.425) (b)
(x = 0.625, y = 0.05, z = 0.325) (c)
(x = 0.75, y = 0.05, z = 0.20) (d)
(x = 0.75, y = 0.15, z = 0.10) (e)
(x = 0.50, y = 0.40, z = 0.10) (f)
(x = 0.15, y = 0.70, z = 0.15) (g)
______________________________________
on the triangular ternary-system diagram; and wherein part of Pb.sup.2+
ions of the main constituent are substituted with 0.01 to 25 mole % of
calcium ions (Ca.sup.2+).
6. The ceramic composition of claim 5 wherein the amount of the Ca.sup.2+
-substitution ranges from 2 to 20 mole %.
7. The ceramic composition of claim 1 wherein the amount of Sr.sup.2+
substituted is about 2, 10 or 30 mole %.
8. The ceramic composition of claim 3 wherein the amount of Ba.sup.2+
substituted is 5, 10 or 25 mole %.
9. The ceramic composition of claim 5 wherein the amount of Ca.sup.2+
substituted is 5, 10 or 25 mole %.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic composition and in particular to
a ceramic composition which has a high dielectric constant and insulation
resistance, a low rate of variation in dielectric constant with
temperature and a low decrease in dielectric constant upon application of
a DC bias.
2. Description of the Prior Art
When a multilayer capacitor is produced from a ceramic composition, the
ceramic composition should be selected so that it satisfies several
requirements. The composition should have a dielectric constant and a
specific resistivity as high as possible and that a rate of variation in
dielectric constant with temperature, dielectric loss and drop in
dielectric constant due to DC bias application should be as low as
possible. Among ceramic compositions having high dielectric constants,
those mainly comprising barium titanate (BaTiO.sub.3) are well known.
However, these compositions require a high sintering temperature.
Accordingly, an additive such as calcium titanate (CaTiO.sub.3) or lead
titanate (PbTiO.sub.3) is incorporated to improve temperature-dependent
characteristics. However the sintering temperature thereof is still on the
order of not less than 1300.degree. C. For this reason, when the ceramic
composition mainly comprising barium titanate is used in making a
multilayer ceramic capacitor, materials for internal electrodes thereof
are limited to, for example, noble metals (e.g., platinum and palladium)
which can withstand such a high sintering temperature. Further, the
dielectric constant achieved by these dielectric ceramic compositions is
at highest about 8000. The dielectric constant thereof may be increased,
but, at a cost of temperature stability. More specifically, these ceramic
compositions simply satisfy Y5V characteristics (-30.degree. to 85.degree.
C.; +22%, -82%) as defined in the EIA Standards.
Although a ceramic material showing a low rate of variation in dielectric
constant with temperature can be produced from the conventional material,
the dielectric constant of the resulting ceramic composition is too low
(on the order of about 2000) to use as a material for capacitors.
To reduce the expenses for producing multilayer ceramic capacitors, it is
necessary to develop a ceramic composition capable of being sintered at a
low temperature on the order of not more than 1150.degree. C., and which
uses less expensive materials for internal electrodes of capacitors such
as those mainly comprising silver or nickel. Recently, there have been
proposed various lead-based composite perovskite type compounds having low
sintering temperatures and high dielectric constants. For instance, a
ternary composition comprising lead magnesium niobate
[Pb(Mg1/3Nb2/3)O.sub.3 ], lead nickel niobate [Pb(Ni1/3Nb2/3)O.sub.3 ] and
lead titanate (PbTiO.sub.3) can achieve a dielectric constant at room
temperature of not less than 10000 (see U.S. Pat. No. 4,712,156). However,
this three-component system suffers from a problem of high
temperature-dependency of the dielectric constant. Moreover, the
capacitances thereof are greatly reduced upon application of a DC bias and
correspondingly, the resulting capacitors are greatly limited in their
practical applications.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a ceramic
composition which comprises the foregoing three-component system and
exhibits a high dielectric constant on the order of not less than 10000, a
substantially improved temperature-dependency thereof and a small drop in
capacitance upon application of a DC bias.
The foregoing and other objects and features of the present invention will
be apparent from the following description.
According to the present invention, there is provided a ceramic composition
which comprises, as a main constituent, a ternary system essentially
consisting of lead magnesium niobate [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ],
lead nickel niobate, [Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ] and lead titanate
[PbTiO.sub.3 ] and being expressed by the following general formula:
[Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z wherein the subscripts x,
y and z satisfy the following relation: x+y+z=1.0 and fall within the
range defined by and be on the line segments joining the following seven
points (a) to (g) which are given by the coordinates:
______________________________________
(x = 0.10, y = 0.70, z = 0.20) (a)
(x = 0.10, y = 0.475, z = 0.425) (b)
(x = 0.625, y = 0.05, z = 0.325) (c)
(x = 0.75, y = 0.05, z = 0.20) (d)
(x = 0.75 y = 0.15, z = 0.10) (e)
(x = 0.50, y = 0.40, z = 0.10) (f)
(x = 0.15, y = 0.70, z = 0.15) (g)
______________________________________
on the triangular ternary-system diagram; and wherein part of lead ions
(Pb.sup.2+) of the main constituent are substituted with 0.01 to 30 mole %
of strontium ions (Sr.sup.2+), 0.01 to 25 mole % of barium ions
(Ba.sup.2+) or 0.01 to 25 mole % of calcium ions (Ca.sup.2+)
BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is the ternary-system diagram for Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
-Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -PbTiO.sub.3 showing the acceptable
compositional range of the main constituent of the ceramic composition of
the present invention;
FIG. 2 is a graph showing the temperature-dependency of the dielectric
constant of an embodiment of the ceramic composition according to the
present invention in which x, y and z are 0.50, 0.30 and 0.20 respectively
and the amount of Sr.sup.2+ -substitution is 0, 10 or 30 mole %;
FIG. 3 is a graph in which the rate of variation in capacitance observed
when a DC bias is applied to a multilayer ceramic capacitor is plotted
against the strength of DC electric field per layer of the capacitor (as
determined in Example 2 and Comparative Example 1);
FIG. 4 is a graph showing the temperature-dependency of the dielectric
constant of a further embodiment of the ceramic composition according to
the present invention in which x, y and z are 0.50, 0.30 and 0.20
respectively and the amount of Ba.sup.2+ substitution is 0, 10 or 25 mole
%;
FIG. 5 is a graph in which the rate of variation in capacitance observed
when a DC bias is applied to a multilayer ceramic capacitor is plotted
against the strength of DC electric field per layer of the capacitor (as
determined in Example 4 and Comparative Example 2);
FIG. 6 is a graph showing the temperature-dependency of the dielectric
constant of a further embodiment of the ceramic composition according to
the present invention in which x, y and z are 0.50, 0.30 and 0.20
respectively and the amount of Ca.sup.2+ -substitution is 0, 10 or 25 mole
%; and
FIG. 7 is a graph in which the rate of variation in capacitance observed
when a DC bias is applied to a multilayer ceramic capacitor is plotted
against the strength of DC electric field per layer of the capacitor (as
determined in Example 6 and Comparative Example 3).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The ternary-system diagram of the Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
-Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -PbTiO.sub.3 system, illustrating the
compositional range of the main constituent of the ceramic composition of
the present invention is shown in FIG. 1. In this figure (a) to (g) are
coordinates in the ternary-system diagram and the acceptable compositional
range is shown as the shadowed portion in the figure including the
boundary lines.
In the ceramic composition of the present invention, the amount of
Sr.sup.2+ ions with which Pb.sup.2+ ions in the main constituent are
substituted ranges from 0.01 to 30 mole %, preferably 2 to 20 mole %; that
of Ba.sup.2+ ions ranges from 0.01 to 25 mole %, preferably 2 to 20 mole
%; and that of Ca.sup.2+ ions ranges from 0.01 to 25 mole %, preferably 2
to 20 mole %.
The present invention will hereinafter be described in more detail with
reference to the following nonlimitative working Examples and the effects
practically achieved by the present invention will also be discussed in
detail in comparison with Comparative Examples.
EXAMPLE 1
In this Example, there were used, as starting materials, lead oxide (PbO),
magnesium oxide (MgO), niobium oxide (Nb.sub.2 O.sub.5), nickel oxide
(NiO), titanium oxide (TiO.sub.2) and strontium carbonate (SrCO.sub.3) and
these starting materials were weighed so as to satisfy the compounding
ratio as shown in Tables 1 to 3.
These weighed starting materials were subjected to wet-milling and mixing
in a ball mill, calcined at 800.degree. to 850.degree. C., followed by
re-milling of the resulting powder in a ball mill, filtration, drying,
addition of an organic binder, sizing and pressing to give two disk-like
samples having a diameter of about 16 mm and a thickness of about 2 mm as
well as a cylindrical sample having a diameter of about 16 mm and a
thickness of about 10 mm. The latter was used in the subsequent
determination of sintering density.
Then the pressed disk-like samples were fired at a temperature ranging from
1100.degree. to 1150.degree. C. for one hour. Then silver electrodes were
printed onto both faces of the fired disk-like samples at 600.degree. C.
and the capacitances and dielectric losses thereof were determined at a
frequency of 1 kHz, a voltage of 1 V r.m.s. and room temperature using a
digital LCR meter to obtain the dielectric losses and capacitances
thereof. Moreover, an electric current upon application of a DC voltage of
50 V for one minute to the samples was determined by an insulation
resistance tester to obtain the specific resistivity of each sample. The
dielectric constant was obtained from the capacitance determined. In
addition, capacitances were determined at -30.degree. and 85.degree. C. to
obtain the variation in dielectric constant with temperature as a value
relative to that observed at 20.degree. C.
Tables 1 to 3 show the compounding ratio: x, y and z of the main
constituent: [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of the resulting ceramic
composition and the amount of Sr.sup.2+ ions with which Pb.sup.2+ ions
in the main constituent were substituted, and Tables 4 to 6 show the
dielectric constant as determined at room temperature, the dielectric
loss, the specific resistivity and the variations of dielectric constants
(relative to that observed at 20.degree. C.) determined at -30.degree. C.
and 85.degree. C.
In these table, the asterisk (*) means that the compounding ratio of the
main constituent of the corresponding sample is beyond the range defined
in the present invention and the double asterisk (**) means that the
amount of Sr.sup.2+ -substitution thereof is beyond the range defined in
the present invention.
TABLE 1
______________________________________
Compounding Ratios of Sample Nos. 1 to 20
Amount
of Sr.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
1* 80 0 20 10
2** 75 15 10 0
3 75 15 10 2
4 75 15 10 10
5** 75 5 20 0
6 75 5 20 10
7 75 5 20 30
8** 65 10 25 0
9 65 10 25 10
10** 62.5 5 32.5 0
11 62.5 5 32.5 30
12** 62.5 5 32.5 35
13** 60 20 20 0
14 60 20 20 10
15 60 20 20 30
16* 50 40 10 0
17* 50 40 10 5
18** 50 30 20 0
19 50 30 20 0.01
20 50 30 20 2
______________________________________
TABLE 2
______________________________________
Compounding Ratios of Sample Nos. 21 to 40
Amount
of Sr.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
21 50 30 20 10
22 50 30 20 30
23** 50 20 30 0
24 50 20 30 10
25 50 20 30 30
26* 50 10 40 0
27* 50 10 40 30
28* 50 10 40 40
29** 40 40 20 0
30 40 40 20 0.01
31 40 40 20 10
32** 40 30 30 0
33 40 30 30 10
34 40 30 30 30
35** 30 40 30 0
36 30 40 30 10
37 30 40 30 30
38** 20 50 30 0
39 20 50 30 10
40 20 50 30 30
______________________________________
TABLE 3
______________________________________
Compounding Ratios of Sample Nos. 41 to 52
Amount
of Sr.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
41** 10 67.5 22.5 0
42 10 67.5 22.5 0.01
43 10 67.5 22.5 2
44** 10 47.5 42.5 0
45 10 47.5 42.5 30
46** 10 47.5 42.5 40
47* 5 60 35 0
48* 5 60 35 10
49** 10 70 20 0
50 10 70 20 2
51** 15 70 15 0
52 15 70 15 2
______________________________________
TABLE 4
______________________________________
Properties of Samples Nos. 1 to 20
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
1* 5580 1.5 6.8 .times. 10.sup.10
-60.2 -10.5
2** 22560 7.3 2.1 .times. 10.sup.11
-63.7 -64.5
3 21770 3.8 8.2 .times. 10.sup.11
-54.3 -59.1
4 8560 1.1 1.3 .times. 10.sup.12
-35.2 -55.1
5** 13710 6.9 1.7 .times. 10.sup.11
-64.1 +57.3
6 12840 2.1 9.8 .times. 10.sup.11
-50.6 -33.1
7 5500 0.5 1.7 .times. 10.sup.13
+2.3 -45.3
8** 10320 7.1 2.6 .times. 10.sup.11
-54.1 +72.1
9 14560 2.3 1.1 .times. 10.sup.12
-54.7 -27.6
10** 8310 7.6 2.9 .times. 10.sup.11
- 52.6 +51.0
11 8680 2.1 2.6 .times. 10.sup.13
-54.3 -47.2
12** 6100 2.5 7.8 .times. 10.sup.12
-46.1 -58.5
13** 16720 6.5 3.1 .times. 10.sup.11
-62.3 +13.7
14 12850 2.0 2.5 .times. 10.sup.12
-54.1 -32.6
15 7240 0.7 2.9 .times. 10.sup.13
-35.2 -15.6
16* 15200 3.1 3.0 .times. 10.sup.11
-56.5 -70.3
17* 6800 0.5 1.9 .times. 10.sup.12
+11.5 -61.5
18** 17080 6.9 3.9 .times. 10.sup.11
-68.5 -5.2
19 19560 2.7 9.1 .times. 10.sup.11
-57.1 -27.4
20* 20500 1.2 2.7 .times. 10.sup.12
-54.5 -41.1
______________________________________
TABLE 5
______________________________________
Properties of Samples Nos. 21 to 40
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
21 14100 0.4 6.1 .times. 10.sup.12
-8.5 -54.8
22 7320 0.1 2.0 .times. 10.sup.13
+15.8 -50.1
23** 10240 6.5 4.9 .times. 10.sup.11
-21.5 +41.5
24 12180 3.2 6.7 .times. 10.sup.12
-50.8 +2.3
25 8680 0.9 1.9 .times. 10.sup.13
-52.6 -43.6
26* 6120 6.3 4.5 .times. 10.sup.11
-20.3 +85.1
27* 6420 4.9 2.2 .times. 10.sup.13
-37.6 +40.5
28* 4270 3.7 2.0 .times. 10.sup.13
-48.3 -11.5
29* 18700 6.7 4.1 .times. 10.sup.11
-62.6 -18.3
30 19150 3.9 8.2 .times. 10.sup.11
-57.3 -25.8
31 10400 0.2 2.7 .times. 10.sup.12
-15.8 -53.8
32** 8650 6.8 4.3 .times. 10.sup.11
-29.8 +36.3
33 11300 3.6 3.6 .times. 10.sup.12
-37.5 +11.2
34 8640 0.9 2.8 .times. 10.sup.13
-49.7 -40.5
35** 12510 7.0 4.6 .times. 10.sup.11
-41.7 +61.3
36 10800 4.1 3.4 .times. 10.sup.12
-56.8 +20.6
37 9790 1.0 3.0 .times. 10.sup.13
-47.3 -50.5
38** 13300 6.8 4.5 .times. 10.sup.11
-50.7 +81.3
39 13850 4.6 3.1 .times. 10.sup.12
-49.6 +19.6
40 9230 0.3 3.4 .times. 10.sup.13
-40.6 -44.8
______________________________________
TABLE 6
______________________________________
Properties of Samples Nos. 41 to 52
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
41** 24510 3.1 5.8 .times. 10.sup.11
-71.4 -67.8
42 21400 2.9 8.6 .times. 10.sup.11
-60.3 -61.2
43 18740 1.8 1.7 .times. 10.sup.12
-48.1 -55.8
44** 7210 7.5 6.0 .times. 10.sup.11
-36.5 +39.3
45 10800 2.1 2.2 .times. 10.sup.13
-52.6 -45.5
46** 5320 1.2 8.6 .times. 10.sup.12
-41.5 -57.2
47* 7220 6.5 5.7 .times. 10.sup.11
-46.5 +42.6
48* 6830 4.7 9.3 .times. 10.sup.11
-52.8 +3.7
49** 9500 4.2 6.5 .times. 10.sup.12
-52.3 -43.2
50 7960 0.9 8.8 .times. 10.sup.12
-30.9 -39.7
51** 16250 2.3 4.3 .times. 10.sup.12
-53.8 -41.2
52 12240 1.0 7.3 .times. 10.sup.12
-34.6 -38.8
______________________________________
Moreover, to make clear the effect of Sr.sup.2+ -substitution, there is
shown, in FIG. 2, the temperature-dependency of the dielectric constant of
a ceramic composition whose compounding ratio (x, y, z) was (0.50, 0.30,
0.20) and in which the amount of Sr.sup.2+ -substitution was 0, 10 or 30
mole %.
As seen from the data shown in FIG. 2, there is observed a dielectric
constant-depressing effect due to the Sr.sup.2+ -substitution and
accordingly the Curie point of the main constituent is shifted towards the
lower temperature side. Further, as seen from the data listed in Tables 1
to 6, the composition of the present invention in which part of the
Pb.sup.2+ ions in the main constituent, a ternary system essentially
consisting of [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ]-[Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ]-[PbTiO.sub.3 ], is substituted with Sr.sup.2+ ions
has high dielectric constant and specific resistivity at room temperature
as well as a low variation in dielectric constant with temperature and
thus can satisfy the Y5U characteristics (-30.degree. to 85.degree. C.;
+22%, -56%) as defined in the EIA Standards. Furthermore, the composition
of the present invention can be sintered at a relatively low temperature
on the order of not more than 1150.degree. C. and correspondingly a
silver-palladium alloy can be used as a material for the internal
electrodes of multilayer ceramic capacitors.
EXAMPLE 2
The same procedures used in Example 1 were repeated to give a dielectric
powder except that lead oxide, magnesium oxide, titanium oxide, nickel
oxide, niobium oxide and strontium carbonate were correctly dispensed so
that the resulting dielectric powder had a compounding ratio: (x, y, z) in
the main ingredient represented by [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
].sub.x [Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub. y [PbTiO.sub.3 ].sub.z of
(0.50, 0.30, 0.20) and 10 mole % of Pb.sup.2+ ions were substituted with
Sr.sup.2+ ions.
The resulting dielectric powder was dispersed in an organic solvent,
kneaded with an organic binder to give a slurry and the resulting slurry
was formed into a film having a thickness of 40 .mu.m according to the
doctor blade technique currently used. Then a paste for an internal
electrode was printed on the film in accordance with the usual screen
printing method, followed by stamping out the film into a desired shape,
lamination, hot-pressing to give a multilayer body which was then cut into
pieces having a desired shape to obtain green chips for capacitors. The
resulting green chips were heated to desired temperatures to remove the
binder and to fire and then a silver paste was applied thereto to form
external electrodes.
The capacitance of the capacitor was determined at room temperature by
applying an alternating current having a frequency of 1 kHz and a voltage
of 1 V r.m.s. using a digital LCR meter while a DC bias of 0 to 50 V was
applied to the multilayer ceramic capacitor with a digital multi meter.
The results thus obtained are plotted in FIG. 3.
COMPARATIVE EXAMPLE 1
The same procedures used in Example 2 were repeated except for using a
composition having the compounding ratio (x, y, z) in the main constituent
represented by [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of (0.20, 0.60, 0.20) and
free of Sr.sup.2+ -substitution to give a capacitor and the capacitance
thereof upon applying a DC bias was determined in the same manner
described in Example 2. The results obtained are plotted in FIG. 3
together with the results obtained in Example 2.
The results shown in FIG. 3 clearly indicate that the capacitor obtained
from the ceramic composition of the present invention in which part of
Pb.sup.2+ ions in the main constituent was substituted with Sr.sup.2+
ions has the DC bias characteristics superior to those for the capacitor
obtained using the compositions of Comparative Example 1, which was free
of Sr.sup.2+ -substitution.
EXAMPLE 3
In this example, there were used, as starting materials, lead oxide (PbO),
magnesium oxide (MgO), niobium oxide (Nb.sub.2 O.sub.5), nickel oxide
(NiO), titanium oxide (TiO.sub.2) and barium carbonate (BaCO.sub.3) and
these starting materials were weighed so as to satisfy the compounding
ratio as shown in Tables 7 to 9.
These weighed starting materials were subjected to wet-milling and mixing
in a ball mill, calcined at 800.degree. to 850.degree. C., followed by
re-milling of the resulting powder in a ball mill, filtration, drying,
addition of an organic binder, sizing and pressing to give two disk-like
samples having a diameter of about 16 mm and a thickness of about 2 mm and
a cylindrical sample having a diameter of about 16 mm and a thickness of
about 10 mm. The latter was used in the subsequent determination of
sintering density.
Then the pressed disk-like samples were fired at a temperature ranging from
1100.degree. to 1150.degree. C. for one hour. Silver electrodes were
printed onto both faces of the fired disk-like samples at 600.degree. C.
and the capacitances and dielectric losses thereof were determined at a
frequency of 1 kHz, an AC voltage of 1 V r.m.s. and room temperature using
a digital LCR meter. Then a current upon application of a DC voltage of 50
V to the samples for one minute was determined using an insulation
resistance tester to determine specific resistivities of the samples. The
dielectric constant was obtained from the capacitance determined above.
Further, the capacitances at -30.degree. and 85.degree. C. were determined
to obtain variations in dielectric constants in terms of values relative
to that observed at 20.degree. C.
Tables 7 to 9 show the compounding ratio: x, y and z of the main
constituent: [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of the resulting ceramic
composition and the amount of Ba.sup.2+ -substitution (mole %) and Tables
10 to 12 show the dielectric constant at room temperature, the dielectric
loss, the specific resistivity and the variations of dielectric constants
determined at -30.degree. C. and 85.degree. C. (in terms of values
relative to that observed at 20.degree. C.) which were determined in this
Example.
In these tables, the asterisk (*) means that the compounding ratio of the
main constituent of the corresponding sample is beyond the range defined
in the present invention and double asterisk (**) means that the amount of
Ba.sup.2+ -substitution is beyond the range defined in the present
invention.
TABLE 7
______________________________________
Compounding Ratios of Sample Nos. 1 to 20
Amount
of Ba.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
1* 80 0 20 10
2** 75 15 10 0
3 75 15 10 1
4 75 15 10 5
5** 75 5 20 0
6 75 5 20 10
7 75 5 20 25
8** 65 10 25 0
9 65 10 25 10
10** 62.5 5 32.5 0
11 62.5 5 32.5 25
12** 62.5 5 32.5 30
13** 60 20 20 0
14 60 20 20 5
15 60 20 20 10
16 60 20 20 25
17* 50 40 10 0
18* 50 40 10 2
19** 50 30 20 0
20 50 30 20 0.01
______________________________________
TABLE 8
______________________________________
Compounding Ratios of Sample Nos. 21 to 40
Amount
of Ba.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
21 50 30 20 2
22 50 30 20 10
23 50 30 20 25
24** 50 20 30 0
25 50 20 30 10
26 50 20 30 25
27* 50 10 40 0
28* 50 10 40 25
29* 50 10 40 30
30** 40 40 20 0
31 40 40 20 0.01
32 40 40 20 10
33** 40 30 30 0
34 40 30 30 10
35 40 30 30 25
36** 30 40 30 0
37 30 40 30 10
38 30 40 30 25
39** 20 50 30 0
40 20 50 30 10
______________________________________
TABLE 9
______________________________________
Compounding Ratios of Sample Nos. 41 to 52
Amount
of Ba.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
41 20 50 30 25
42** 10 67.5 22.5 0
43 10 67.5 22.5 2
44** 10 47.5 42.5 0
45 10 47.5 42.5 25
46** 10 47.5 42.5 30
47* 5 60 35 0
48* 5 60 35 10
49** 10 70 20 0
50 10 70 20 2
51** 15 70 15 0
52 15 70 15 2
______________________________________
TABLE 10
______________________________________
Properties of Samples Nos. 1 to 20
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
1* 7630 3.8 7.9 .times. 10.sup.10
-59.3 -22.5
2** 22560 7.3 2.1 .times. 10.sup.11
-63.7 -64.5
3 20810 4.1 6.3 .times. 10.sup.11
-55.3 -58.1
4 12340 1.9 1.1 .times. 10.sup.12
-52.6 -51.2
5** 13710 6.9 1.7 .times. 10.sup.11
-64.1 +57.3
6 11530 2.3 7.7 .times. 10.sup.11
-57.3 -21.7
7 8150 0.9 6.5 .times. 10.sup.12
-38.1 -48.6
8** 10320 7.1 2.6 .times. 10.sup.11
-54.1 +72.1
9 12800 2.6 9.0 .times. 10.sup.11
-49.2 -7.6
10** 8310 7.6 2.9 .times. 10.sup.11
- 52.6 +51.0
11 9560 2.7 1.3 .times. 10.sup.13
-48.7 -26.3
12** 7630 3.1 7.2 .times. 10.sup.12
-49.3 -53.6
13** 16720 6.5 3.1 .times. 10.sup.11
-62.3 +13.7
14 12380 2.9 8.3 .times. 10.sup.11
-45.6 -39.5
15 9710 2.2 1.6 .times. 10.sup.12
-40.3 -32.1
16 7320 1.1 1.4 .times. 10.sup.13
+16.4 -51.6
17* 15200 3.1 3.0 .times. 10.sup.11
-56.5 -70.3
18* 8150 2.6 5.6 .times. 10.sup.11
-27.5 -67.1
19** 17080 6.9 3.9 .times. 10.sup.11
-68.5 -5.2
20 18320 3.2 7.7 .times. 10.sup.11
-55.7 -31.7
______________________________________
TABLE 11
______________________________________
Properties of Samples Nos. 21 to 40
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
21 20040 2.0 1.4 .times. 10.sup.12
-58.3 -47.5
22 15300 1.1 3.8 .times. 10.sup.12
-37.9 -55.8
23 7310 0.3 9.6 .times. 10.sup.12
+20.5 -52.1
24** 10240 6.5 4.0 .times. 10.sup.11
-21.5 +41.5
25 12070 3.9 2.1 .times. 10.sup.12
-53.3 +32.6
26 7160 1.1 8.4 .times. 10.sup.12
-44.4 -43.8
27* 6120 6.3 4.5 .times. 10.sup.11
-20.3 +85.1
28* 5680 5.1 6.8 .times. 10.sup.12
-43.9 +40.4
29* 5210 3.9 8.2 .times. 10.sup.12
-46.2 +25.0
30** 18700 6.7 4.1 .times. 10.sup.11
-62.6 -18.3
31 19620 4.2 7.4 .times. 10.sup.11
-59.8 -24.5
32 11270 0.7 2.2 .times. 10.sup.12
-42.5 -55.8
33** 8560 6.8 4.3 .times. 10.sup.11
-29.8 +36.3
34 10890 3.9 2.7 .times. 10.sup.12
-49.5 +14.7
35 8220 1.1 1.5 .times. 10.sup.13
-51.2 -54.1
36** 12510 7.0 4.6 .times. 10.sup.11
-41.7 +61.3
37 11980 4.7 2.1 .times. 10.sup.12
-50.2 -11.6
38 7330 1.9 1.8 .times. 10.sup.13
-34.2 -56.1
39** 13300 6.8 4.5 .times. 10.sup.11
-50.7 +81.3
40 14550 4.8 2.1 .times. 10.sup.12
-55.1 -20.7
______________________________________
TABLE 12
______________________________________
Properties of Samples Nos. 41 to 52
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
41 6980 0.7 1.7 .times. 10.sup.13
+3.3 -54.3
42** 24510 3.1 5.8 .times. 10.sup.11
-71.4 -67.8
43 17630 1.9 9.6 .times. 10.sup.11
-53.6 -54.5
44** 7210 7.5 6.0 .times. 10.sup.11
-36.5 +39.3
45 8160 3.8 8.3 .times. 10.sup.12
-51.2 -32.9
46** 6240 3.1 9.6 .times. 10.sup.12
-44.8 -53.2
47* 7220 6.5 5.7 .times. 10.sup.11
-46.5 +42.6
48* 8740 5.0 8.3 .times. 10.sup.11
-58.6 +9.1
49** 8500 4.2 6.5 .times. 10.sup.12
-52.3 -43.2
50 8410 1.7 8.1 .times. 10.sup.12
-34.6 - 39.4
51** 16250 2.3 4.3 .times. 10.sup.12
-53.8 -41.2
52 13060 1.3 6.5 .times. 10.sup.12
-40.8 -37.2
______________________________________
Moreover, to make clear the effect of Ba.sup.2+ -substitution, there is
shown, in FIG. 4, the temperature-dependency of the dielectric constant of
a ceramic composition whose compounding ratio (x, y, z) was (0.50, 0.30,
0.20) and in which the amount of Ba.sup.2+ -substitution was 0, 10 or 25
mole %.
As seen from the data shown in FIG. 4, there is observed a dielectric
constant-depressing effect of the Ba.sup.2+ -substitution and accordingly
the Curie point of the main constituent is shifted towards the lower
temperature side. Further, as seen from the data listed in Tables 7 to 12,
the composition of the present invention in which part of Pb.sup.2+ in
the main constituent, a ternary system essentially consisting of
[Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ]-[Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
]-[PbTiO.sub.3 ], is substituted with Ba.sup.2+ ions has a high
dielectric constant and specific resistivity at room temperature as well
as a low variation in dielectric constant with temperature and thus can
satisfy the Y5U characteristics (-30.degree. to 85.degree. C.; +22%, -56%)
as defined in the EIA Standards. Furthermore, the composition of the
present invention can be sintered at a relatively low temperature in the
order of not more than 1150.degree. C. and correspondingly a
silver-palladium alloy can be used as a material for the internal
electrodes of multilayer ceramic capacitors.
EXAMPLE 4
The same procedures used in Example 3 were repeated to give a dielectric
powder except that lead oxide, magnesium oxide, titanium oxide, nickel
oxide, niobium oxide and barium carbonate were correctly weighed so that
the resulting dielectric powder had a compounding ratio: (x, y, z) in the
main constituent represented by [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x
[Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of (0.50,
0.30, 0.20) and 10 mole % of Pb.sup.2+ ions were substituted with
Ba.sup.2+ ions.
The resulting dielectric powder was dispersed in an organic solvent,
kneaded with an organic binder to give a slurry and the resulting slurry
was formed into a film having a thickness of 40 .mu.m according to the
doctor blade technique currently used. Then a paste for an internal
electrode was printed on the film in accordance with the usual screen
printing method, followed by stamping out the film into a desired shape,
lamination, hot-pressing to give a multilayer body which was then cut into
pieces having a desired shape to obtain green chips for capacitors. The
resulting green chips were heated to desired temperatures to remove the
binder and to fire and then silver paste was applied thereto to form
external electrodes.
The capacitance of the capacitor was determined at room temperature by
applying an alternating current having a frequency of 1 kHz and a voltage
of 1 V r.m.s. using a digital LCR meter while a DC bias of 0 to 50 V was
applied to the multilayer ceramic capacitor with a digital multi meter.
The results thus obtained are plotted in FIG. 5.
COMPARATOR EXAMPLE 2
The same procedures used in Example 4 were repeated except for using a
composition having the compounding ratio (x, y, z) in the main constituent
represented by Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of (0.20, 0.60, 0.20) and
free of Ba.sup.2+ -substitution to give a capacitor and the capacitance
thereof upon applying a DC bias was determined in the same manner
described in Example 4. The results obtained are plotted in FIG. 5
together with the results obtained in Example 4.
The results shown in FIG. 5 clearly indicate that the capacitor obtained
from the ceramic composition of the present invention in which part of the
Pb.sup.2+ ions in the main constituent was substituted with Ba.sup.2+
ions shows the behavior upon application of a DC bias superior to that for
the capacitor obtained using the composition of Comparative Example 2,
which is free of Ba.sup.2+ -substitution.
EXAMPLE 5
In this Example, there were used, as starting materials, lead oxide (PbO),
magnesium oxide (MgO), niobium oxide (Nb.sub.2 O.sub.5), nickel oxide
(NiO), titanium oxide (TiO.sub.2) and calcium carbonate (CaCO.sub.3) and
these starting materials were weighed so as to satisfy the compounding
ratio as shown in Tables 13 to 15.
These dispensed starting materials were subjected to wet-milling and mixing
in a ball mill, calcined at 800.degree. to 850.degree. C., followed by
re-milling of the resulting powder in a ball mill, filtration, drying,
addition of an organic binder, sizing and pressing to give two disk-like
samples having a diameter of about 16 mm and a thickness of about 2 mm and
a cylindrical sample having a diameter of about 16 mm and a thickness of
about 10 mm. The latter was used in the subsequent determination of
sintering density.
Then the pressed disk-like samples were fired at a temperature ranging from
1100.degree. to 1150.degree. C. for one hour. Silver electrodes were
printed onto both faces of the fired disk-like samples at 600.degree. C.
and the capacitances and dielectric losses thereof were determined at a
frequency of 1 kHz, a voltage of 1 V r.m.s. and room temperature using a
digital LCR meter. Then a current upon application of a DC voltage of 50 V
to the samples for one minute was determined using an insulation
resistance tester to determine specific resistivity of the samples. The
dielectric constant was obtained from the capacitance determined above.
Further, the capacitances at -30.degree. and 85.degree. C. were determined
to obtain variations in dielectric constants in terms of values relative
to that observed at 20.degree. C.
Tables 13 to 15 show the compounding ratio: x, y and z of the main
constituent: [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of the resulting ceramic
composition, and the amount of Ca.sup.2+ -substitution (mole %) and Tables
16 to 18 show the dielectric constant at room temperature, the dielectric
loss, the specific resistivity and the variations of dielectric constants
determined at -30.degree. C. and 85.degree. C. (in terms of values
relative to that observed at 20.degree. C.) which were determined in this
example.
In these tables, the asterisk (*) means that the compounding ratio of the
main constituent of the corresponding sample is beyond the range defined
in the present invention and double asterisk (**) means that the amount of
Ca.sup.2+ -substitution is beyond the range defined in the present
invention.
TABLE 13
______________________________________
Compounding Ratios of Sample Nos. 1 to 20
Amount
of Ca.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
1* 80 0 20 10
2** 75 15 10 0
3 75 15 10 1
4 75 15 10 5
5** 75 5 20 0
6 75 5 20 10
7 75 5 20 25
8** 65 10 25 0
9 65 10 25 10
10** 62.5 5 32.5 0
11 62.5 5 32.5 25
12** 62.5 5 32.5 30
13** 60 20 20 0
14 60 20 20 5
15 60 20 20 10
16 60 20 20 25
17* 50 40 10 0
18* 50 40 10 2
19** 50 30 20 0
20 50 30 20 0.01
______________________________________
TABLE 14
______________________________________
Compounding Ratios of Sample Nos. 21 to 40
Amount
of Ca.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
21 50 30 20 2
22 50 30 20 10
23 50 30 20 25
24** 50 20 30 0
25 50 20 30 10
26 50 20 30 25
27* 50 10 40 0
28* 50 10 40 25
29* 50 10 40 30
30** 40 40 20 0
31 40 40 20 0.01
32 40 40 20 10
33** 40 30 30 0
34 40 30 30 10
35 40 30 30 25
36** 30 40 30 0
37 30 40 30 10
38 30 40 30 25
39** 20 50 30 0
40 20 50 30 10
______________________________________
TABLE 15
______________________________________
Compounding Ratios of Sample Nos. 41 to 52
Amount
of Ca.sup.2+ -
Sample
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3
Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3
PbTiO.sub.3
Substitution
No. (mole %) (mole %) (mole %)
(mole %)
______________________________________
41 20 50 30 25
42** 10 67.5 22.5 0
43 10 67.5 22.5 2
44** 10 47.5 42.5 0
45 10 47.5 42.5 25
46** 10 47.5 42.5 30
47* 5 60 35 0
48* 5 60 35 10
49** 10 70 20 0
50 10 70 20 2
51** 15 70 15 0
52 15 70 15 2
______________________________________
TABLE 15
______________________________________
Properties of Samples Nos. 1 to 20
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
1* 8600 4.1 9.8 .times. 10.sup.13
-57.2 -25.6
2** 22560 7.3 2.1 .times. 10.sup.11
-63.7 -64.5
3 25350 5.6 3.1 .times. 10.sup.11
-64.8 -66.4
4 16400 1.6 8.5 .times. 10.sup.11
-41.6 -55.8
5** 13710 6.9 1.7 .times. 10.sup.11
-64.1 +57.3
6 10560 3.1 6.5 .times. 10.sup.11
-43.1 -39.6
7 6540 1.2 2.1 .times. 10.sup.12
-41.6 -53.9
8** 10320 7.1 2.6 .times. 10.sup.11
-54.1 +72.1
9 12650 5.1 8.1 .times. 10.sup.11
-56.1 -35.6
10** 8310 7.6 2.9 .times. 10.sup.11
-52.6 +51.0
11 6140 4.3 3.6 .times. 10.sup.12
-55.1 +5.8
12** 7520 4.4 1.8 .times. 10.sup.12
-50.8 -21.5
13** 16720 6.5 3.1 .times. 10.sup.11
-62.3 +13.7
14 13500 4.2 6.4 .times. 10.sup.11
-57.0 -37.1
15 10650 1.6 9.6 .times. 10.sup.11
-48.1 -40.5
16 7140 1.1 3.5 .times. 10.sup.12
-11.3 -47.3
17* 15200 3.1 3.0 .times. 10.sup.11
-56.5 -70.3
18* 16340 2.1 5.1 .times. 10.sup.11
-32.5 -61.5
19** 17080 6.9 3.9 .times. 10.sup.11
-68.5 -5.2
20 19160 6.1 4.5 .times. 10.sup.11
-66.7 -12.3
______________________________________
TABLE 17
______________________________________
Properties of Samples Nos. 21 to 40
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
21 21380 5.6 5.8 .times. 10.sup.11
-61.3 -35.4
22 16550 2.1 9.6 .times. 10.sup.11
-41.5 -57.3
23 6860 0.9 2.6 .times. 10.sup.12
+21.5 -45.3
24** 10240 6.5 4.0 .times. 10.sup.11
-21.5 +41.5
25 15320 4.5 1.1 .times. 10.sup.12
-58.0 -5.5
26 9560 1.3 3.3 .times. 10.sup.12
-47.3 -50.6
27* 6120 6.3 4.5 .times. 10.sup.11
-20.3 +85.1
28* 6830 5.5 3.9 .times. 10.sup.12
-43.4 +47.6
29* 5660 4.9 3.1 .times. 10.sup.12
-49.7 +27.9
30** 18700 6.7 4.1 .times. 10.sup.11
-62.6 -18.3
31 20020 5.3 5.6 .times. 10.sup.12
-59.8 -24.6
32 12850 2.0 1.6 .times. 10.sup.12
-31.3 -53.4
33** 8560 6.8 4.3 .times. 10.sup.11
-29.8 +36.3
34 11570 4.2 9.4 .times. 10.sup.11
-51.6 +3.6
35 7960 1.5 5.7 .times. 10.sup.12
-41.5 -53.9
36** 12510 7.0 4.6 .times. 10.sup.11
-41.7 +61.3
37 13810 5.1 9.2 .times. 10.sup.11
-46.6 +8.3
38 8850 2.1 5.8 .times. 10.sup.12
-39.6 -55.0
39** 13300 6.8 4.5 .times. 10.sup.11
-50.7 +81.3
40 15140 5.0 9.6 .times. 10.sup.11
-56.2 -12.4
______________________________________
TABLE 18
______________________________________
Properties of Samples Nos. 41 to 52
tan .delta.
Specific .DELTA..epsilon./.epsilon. (20.degree. C.)
Sample .epsilon.
(20.degree. C.)
Resistivity
-30.degree. C.
85.degree. C.
No. (20.degree. C.)
(%) (.OMEGA. .multidot. cm)
(%) (%)
______________________________________
41 7140 0.8 6.1 .times. 10.sup.12
+8.0 -57.2
42** 24510 3.1 5.8 .times. 10.sup.11
-71.4 -67.8
43 26500 1.6 8.4 .times. 10.sup.12
-68.2 -70.5
44** 7210 7.5 6.0 .times. 10.sup.11
-36.5 +39.3
45 10960 4.9 5.8 .times. 10.sup.12
-52.9 -28.4
46** 8710 5.1 4.2 .times. 10.sup.12
-48.3 -40.1
47* 7220 6.5 5.7 .times. 10.sup.11
-46.5 +42.6
48* 9130 5.2 7.3 .times. 10.sup.11
-60.2 +1.5
49** 8500 4.2 6.5 .times. 10.sup.12
-52.3 -43.2
50 9340 1.2 7.8 .times. 10.sup.12
-31.4 -41.3
51** 16250 2.3 4.3 .times. 10.sup.12
-53.8 -41.2
52 13850 1.1 5.7 .times. 10.sup.12
-37.9 -40.7
______________________________________
Moreover, to make clear the effect of Ca.sup.2+ -substitution, there is
shown, in FIG. 6, the temperature-dependency of the dielectric constant of
a ceramic composition whose compounding ratio (x, y, z) was (0.50, 0.30,
0.20) and in which the amount of Ca.sup.2+ -substitution was 0, 10 or 25
mole %.
As seen from the data shown in FIG. 6, there is observed a dielectric
constant-depressing effect of the Ca.sup.2+ -substitution and accordingly
the Curie point of the main constituent is shifted towards the lower
temperature side. Further, as seen from the data listed in Tables 13 to
18, the composition of the present invention in which part of the
Pb.sup.2+ ions in the main constituent, a ternary system essentially
consisting of [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ]-[Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ]-[PbTiO.sub.3 ], is substituted with Ca.sup.2+ ions
have a high dielectric constant and specific resistivity at room
temperature as well as a low variation in dielectric constant with
temperature and thus can satisfy the Y5U characteristics (-30.degree. to
85.degree. C.; +22%, -56%) as defined in the EIA Standards. Furthermore,
the composition of the present invention can be sintered at a relatively
low temperature in the order of not more than 1150.degree. C. and
correspondingly a silver-palladium alloy can be used as a material for the
internal electrodes of multilayer ceramic capacitors.
EXAMPLE 6
The same procedures used in Example 5 were repeated to give a dielectric
powder except that lead oxide, magnesium oxide, titanium oxide, nickel
oxide, niobium oxide and calcium carbonate were correctly weighed so that
the resulting dielectric powder had a compounding ratio: (x, y, z) in the
main constituent represented by [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3).sub.x
[Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 .sub.z of (0.50,
0.30, 0.20) and 10 mole % of Pb.sup.2+ ions were substituted with
Ca.sup.2+ ions.
The resulting dielectric powder was dispersed in an organic solvent,
kneaded with an organic binder to give a slurry and the resulting slurry
was formed into a film having a thickness of 40 .mu.m according to the
doctor blade technique currently used. Then a paste for an internal
electrode was printed on the film in accordance with the usual screen
printing method, followed by stamping out the film into a desired shape,
lamination, hot-pressing to give a multilayer body which was then cut into
pieces having a desired shape to obtain green chips for capacitors. The
resulting green chips were heated to desired temperatures to remove the
binder and to fire and then a silver paste was applied thereto to form
external electrodes.
The capacitance of the capacitor was determined at room temperature by
applying an alternating current having a frequency of 1 kHz and a voltage
of 1 V r.m.s. using a digital LCR meter while a DC bias of 0 to 50 V was
applied to the multilayer ceramic capacitor with a digital multi meter.
The results thus obtained are plotted in FIG. 7.
COMPARATIVE EXAMPLE 3
The same procedures used in Example 6 were repeated except for using a
composition having the compounding ratio (x, y, z) in the main constituent
represented by [Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 ].sub.x [Pb(Ni.sub.1/3
Nb.sub.2/3)O.sub.3 ].sub.y [PbTiO.sub.3 ].sub.z of (0.20, 0.60, 0.20) and
free of Ca.sup.2+ -substitution to give a capacitor and the capacitance
thereof upon applying a DC bias was determined in the same manner
described in Example 6. The results obtained are plotted in FIG. 7
together with the results obtained in Example 6.
The results shown in FIG. 7 clearly indicate that the capacitor obtained
from the ceramic composition of the present invention in which part of
Pb.sup.2+ ions in the main constituent was substituted with Ca.sup.2+
ions shows the behavior upon application of a DC bias superior to that for
the capacitor obtained using the composition of Comparative Example 3,
which was free of Ca.sup.2+ -substitution.
Incidentally, the Curie points of ceramic compositions whose main
constituents are beyond the range defined in the present invention are
deviated from room temperature to the temperature side much higher or
lower than room temperature and, therefore, such compositions suffer from
such a problem that the dielectric constants thereof at room temperature
are very low, that the temperature-dependency of the dielectric constant
is high within the practical temperature range or that the specific
resistivities thereof are low. Moreover, if the amount of Sr.sup.2+ -,
Ba.sup.2+ - or Ca.sup.2+ -substitution is beyond each corresponding range
defined in the present invention, the resulting composition is not
applicable as a material for use in making capacitors since it suffers
from such a problem that the capacitance is too low or that the Curie
point thereof is greatly deviated from room temperature.
The ceramic composition of the present invention has a high dielectric
constant at room temperature and a low temperature-dependency of
dielectric constant, which can be achieved through the substitution of
Pb.sup.2+ ions in the main constituent with a predetermined amount of
Sr.sup.2+, Ba.sup.2+ or Ca.sup.2+ ions since such ion-substitution
permits the shift of the Curie point of the main constituent towards the
low temperature side and the depression of the temperature-dependency of
dielectric constant. Further, the ceramic composition of the invention
shows a low decrease in the capacitance upon application of a DC bias and
has a specific resistivity higher than that of the composition free of the
substitution of Pb.sup.2+ ions. Thus, the ceramic composition makes it
possible to provide a multilayer ceramic capacitor having excellent
temperature-dependency of dielectric constant and high reliability.
Further, the firing temperature thereof is not more than 1150.degree. C.
and this allows the use of silver-palladium alloys as a material for
internal electrodes of capacitors. The composition is likewise applicable
to such a multilayer ceramic capacitor as a switching power source which
is used while applying a DC bias since the decrease in the capacitance
upon application of a DC bias is relatively small as has already been
discussed above.
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